As shown in FIG. 1, a light emitting diode (LED) backlight driving circuit of a liquid crystal display (LCD) device includes a power supply 10, and an LED lightbar 20 coupled to the power supply 10. A constant current driving chip 30 is used to control brightness of the LED lightbar 20, and an external pulse-width modulation (PWM) dimming signal is sent to the constant current driving chip 30. When the PWM dimming signal is at a high level, current flows through the LED lightbar 20, and when the PWM dimming signal is at a low level, current does not flow through the LED lightbar 20. An average value of the current flowing through the LED lightbar 20 is controlled by adjusting a duty cycle of the PWM dimming signal, thus the brightness of the LED lightbar 20 may be adjusted. A typical PWM dimming method may damage the constant current driving chip 30.